§ 56. TERTIARY STRATA OF NORTH AMERICA. 281 



the relative level of land and water, during the deposition 

 of the marine and fresh-water strata, reviewed in this 

 discourse. 



In North America the researches of Dr. Morton, Professor 

 Vanuxem, Mr. Lvell, and other observers, have shown that 

 in the territories of the United States eocene and miocene de- 

 posits extend over a great part of Maryland, along the coast 

 of New York and New England, and occur in New Jersey, 

 Delaware, Long Island, &c. The tertiary beds of Maryland 

 consist of limestone, clay, sand, and gravel, and abound in 

 the usual eocene shells ; some of which are identical with 

 European tertiary species of turritella, venericardia, fusus, 

 ancilla, &c. The remains of a large cetaceous animal, 

 (named Zeuglodon from its deeply cleft teeth) are found 

 in great numbers in the American eocene deposits.* 



Infusorial marls of Virginia. The towns of Eichmond 

 and Petersburg in Virginia, are built on strata of siliceous 

 marls, which extend over considerable tracts of country, 

 and have an aggregate thickness of more than twenty feet. 

 These marls, whose organic composition was first detected 

 by Professor W. Rogers, are of the older tertiary (miocene 

 or eocene) formations. The investigations of Dr. Bailey 

 have shown, that these earths are almost wholly made up 

 of the siliceous cases, or shields, of infusorial animalcules, 

 termed Navicula, Gaillonella, Actinocyclus, Coscinodis- 

 cus, &c : the latter especially predominate, two or three 

 species forming a large proportion of this aggregation of 

 minute organisms. The Coscinodisci (or sieve-like discs) 

 are elegant saucer-shaped shells, elaborately ornamented 

 with hexagonal spots disposed in curves, and resembling 

 the engine-turned sculpturing on a watch ; they vary in size 

 from 1- 100th to 1 -1000th of an inch in diameter. If but 

 a few grains of the Richmond earth are prepared for the 

 microscope, all the varieties above specified are generally 



* See Medals of Creation, vol. ii, p. 826. 



